Real time color changing of an object
you just need to assign a separate material to that body part, then animate that material color over time, with keyframes

Here is an example of how to do this: the monkey head has a ase blue color, but I assigned a different (grey) material to one ear.

Then at frame 1 I inserted a key frame for the color (press I over the diffuse grey slot), and at frame 80 I changed the color to red, and inserted another keyframe. 

That's it.